Television system



Nov. 1-5, 1938. H. M. LEWIS ET AL. 2,137,123

TELEVISION SYSTEM Filed Oct. 4, 1935 3 Sheets-Sheet l INVENTORS AROLD M. LEWIS, ISON CA EIN.

ATTORN EY NOV. 9 H. M. LEWIS ET AL 2,137,123

TELEVISION SYSTEM Filed Oct. 4, 1955 5 Sheets-Sheet 2 lo 62 lS la 17 GARNER VIDEO CATHODE FREQUENCY DETECTOR FREQUENCY RAY AMPLIFIER AHPLIHER TUBE so 69 7 L mcwmz 7 FREQUENCY GENERATOR 63 A F C I 2 77 7s 68 75 L\ H E 73 FREQUENCY GENERATOR INVENTORS HAROLD M. LEWIS,

BYMDISON CAIN.

ATTORN EY Nov. 15, 193-3. w s ET AL 2,137,123

TELEVISION SYSTEM Filed Oct. 4, 1955 cARmER B2 II VIDEO amma:

FREQUENCY FREQUEHCY95 RAY 0 AMPLIFIER AMPLIFIER TUBE 5 Sheets-Sheet 5 III-1 A.C.C. 5 87 8 9 90 4 I i95 ATFC.

ll PICTURE 96 84 86 FREQUENCY I GEIIERATIIR I LI HE FREQUENCY I GENERATOR 62. v I5 I6 IT I CARRIER VI DEO CATHODE FREQUENCY DETECTOR FREQUENCY RAY 0 AMPLIFIER AMPLIFIER TUBE FREQUENCY II n GENERATOR L I N E FREQUENCY GENERATOR INVENTORS HAROLD M. LEWIS,

BY MZDISON ATTORNEY Patented Nov. 15, 1938 PTENT TELEVISION SYSTEM Harold M. Lewis, Douglaston, Long Island, and Madison Cawein, Manhasset, N. Y., assignors to Hazeltine Corporation, a corporatlon of Delaware Application October 4, 1935, Serial No. 43,548

11 Claims.

to methods of, and apparatus for, automatically" 5 controlling such systems to provide improved operation and insure faithful image and sound reproduction.

The invention is especially directed to the automatic control of the background illumination of the fluorescent screen of a cathode-ray tube in a system such as above described, and is further directed to the automatic control, in cooperation with such background illumination control, of the contrast of the picture detail in the reproduced image, as well as the reproduction of sound, in such system.

According to the present practice in television reception, picture signals or video-frequencies corresponding in amplitude to varying values of light and shade in the subject of transmission are applied to the control grid of a cathode-ray tube to vary the intensity of the cathode ray or beam to reproduce the picture detail. For the purpose of scanning the fluorescent screen of the tube, saw-tooth'current or voltage waves are generated in the receiver and are applied so as to produce electrostatic or magnetic fields of sawtooth form, to direct the ray horizontally and vertically and thereby trace the well-known rectilinear scanning pattern on the screen. In order to synchronize the horizontal or line-scanning action and the vertical or picture-scanning action at the receiver with the corresponding actions at the transmitter, the television carrier is modulated by synchronizing impulses at the end of each line period and each picture or frame period, and these impulses are utilized to control or operate the scanning wave generators. In the arrangements of the prior art, it has ordinarily been necessary for these generators to be continuously operative, since without their operation the cathode ray would remain focused on a single spot on the screen, with resultant damage to the tube or, in any event, an intense spot of light onthe screen which would be objectionable to the eye.

A preferred type of modulation for television carrier waves is negative modulation, that is, modulation whereby increases in carrier ampli- 0 tude represent decreases in illumination and synchronizing impulse peaks appear as points of maximum amplitude of the carrier wave exceeding the amplitude necessary to present complete black on the screen.

In a cathode-ray system the background illumination may be controlled by adjusting the potential applied to one or more of the control electrodes, as for instance the control grid, or

-- screen, to vary the intensity of the cathode ray.

When such an adjustment is made to the extent that the cathode ray does not reach the end of the tube with suflicient intensity to illuminate the screen, it may be termed a fade-out adjustment or control and hereinafter the term fadeout control will be employed to express this operation.

In certain proposed television systems, alternate carriers are provided with vision modulation and sound modulation, respectively, for the transmission of both the scene and the sound of a single program by adjacent carriers. In the design for receiving apparatus for such systems, special problems are presented with regard to the prevention of undesirable effects caused by the presence of the sound-modulated waves in the television channel of the receiver and by the presence of vision-modulated waves in the sound channel of the receiver, during tuning.

It will thus be apparent that television reception may be substantially improved by the provision of an automatic control of the cathode ray, whereby the ray will be present with sufficient intensity to illuminate the screen only at such times as a signal of proper type and of sufficient amplitude for reproducing an intelligible image is being received and proper scanning action is being provided. An arrangement providing such a control may be aptly termed an automatic fade-out control" and may be referred to simply as A. F. C.

Ideal operating conditions may be more closely approached by the provision, in cooperation with an automatic fade-out control, of automatic control of the contrast of the picture detail in accordance with the amplitude of the received carrier. Such automatic contrast control may be referred to simply as A. C. C.

Finally, it will also be apparent that, in systems where alternate carriers have sound and vision modulations, respectively, materially improved reception may be obtained by the provision, in cooperation with the automatic fadeout control and the automatic contrast control, of an automatic control of the reproduction of sound, whereby the receiver will be silenced when video-frequencies are present in the sound channel of the receiver, as for instance, during a tuning operation when the sound channel is tuned to a vision-modulated carrier.

It is, therefore, a primary object of this inmeans for, automatically controlling the background illumination in a cathode-ray system in accordance with the characteristics of received vision-modulated carrier waves and with the scanning action of the receiver.

A further object is to provide a method of, and means for, automatically controlling the contrast of the detail of the reproduced image, in cooperation with the above-mentioned type of background illumination control or, automatic fade-out control.

A still further object is to provide a method of, and means for, automatically controlling the reproduction of sound in a receiver designed for the reception of alternate carriers modulated by sound and vision frequencies, respectively, to prevent undesirable effects of vision-modulation frequencies in the sound channel of the receiver.

For a better understanding of our invention, together with other and further objects thereof, reference is had to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In accordance with the present invention, the control of the background illumination, or automatic fade-out control, is accomplished by applying a bias voltage to one of the control electrodes of the cathode-ray system, which voltage is derived by rectification of a modulation component unique to a vision-modulated carrier, or-by rectification of a part of the locally generated scanning impulses controlled by such carrier. Preferably, such control electrode of the cathode-ray system is normally maintained at such a potential that the electron ray is of insuificient intensity to illuminate the screen, and the automatic fade-out control voltage is applied positively to effect illumination of the screen only when the received carrier is of a predetermined amplitude or characteristic to efi'ect proper scanning.

The rectifier for producing the automatic fadeout control voltages may be a separate device, or a single rectifier may be employed to produce both the modulation components of the carrier and unidirectional voltage for the automatic fade-out control.

Further, the rectifier which derives the automatic fade-out control voltage may be connected at various points in the system. Thus, in a preferred embodiment of the invention, the automatic fade-out control rectifier is connected to the output of, or to an appropriate .point in, the line-frequency generator circuit and is thus dependent thereon, so that without proper scanning action there can be no background illumination; in other embodiments, this rectifier is connected to the output of the carrier-frequency amplifier or to the output of the video-frequency amplifier. The systems for producing the automatic fadeout control voltages are made selective, either by virtue of the point in the receiver at which the automatic fade-out control rectifier is connected, as in the first-mentioned embodiment; by the provision of selective circuits in connection therewith; or by virtue of the type of rectification employed, as for instance, peak detection of the synchronizing impulses of the received carrier, to the end that no beam will be present unless a proper signal is being received and/or proper scanning is being effected.

Thus, according to the present invention the screen is illuminated only when a vision-moduvention to provide an improved method of, and

that the screen is scanned under synchronized control, whereby a picture is reproduced; or, in other-words, only signals representing image intelligence may be shown. When a vision-modulated carrier is tuned in, the picture appears, with proper scanning, and when the carrier is "tuned out, the scanning ceases and the picture fades out. Injuries or' undesirable effects which would be occasioned by the stopping of the ray at a spot on the screen are completely obviated and, inasmuch as the screen is darkened in absence of a proper signal, the necessity heretofore present of providing continuously operating scanning generators in order to prevent such injuries and undesirable effects is avoided.

Automatic contrast control is preferably provided in cooperation with the automatic fade-out control by applying to the grids of the carrierfrequency amplifier tubes negative biasing potentials variable in accordance with the intensity of the received carrier, in a manner similar to the automatic amplification control of sound broadcast receivers. The automatic contrast control voltage may be derived from the same rectifier that produces the automatic fade-out control voltages or from a separate rectifier and from the same or different points in the system, as desired.

Also, in a system of the type described, designed for alternate sound and vision carriers, the reproduction of sound is preferably controlled so as to prevent video-frequencies from being reproduced by the sound channel of the receiver, as would otherwise result when the sound channel is tuned through a vision-modulated carrier, This may be accomplished by applying a voltage from the audo-frequency channel to a selecting, amplifying lated signal is tuned in under conditions such and rectifying arrangement to derive therefrom a negative biasing voltage only if and when videofrequencies are present in the sound channel of the receiver. This biasing voltage may be applied to the control grids of the audio-frequency amplifier tubes, or other suitable tubes, to silence the sound reproducer.

In the accompanying drawings, Fig. 1 is a circuit diagram, partly schematic, of a. complete television receiving system embodying the present invention and including both visionand soundmodulated carrier receiving and reproducing channels; Fig. 2a is a graph of the modulation voltage derived by detecting a self-synchronizing type of negatively modulated carrierwave; Fig. 2b is a graph of the unidirectional voltage derived by peak detection of the detected wave shown in Fig. 2a; while Figs. 3, 4 and 5 are circuit diagrams, also partly schematic, of modified forms of the television system of Fig. 1 in which the several automatic control bias voltages are derived from difierent points of the system and/ or by means of common or independent rectifiers.

Referring now particularly to Fig. 1 of the drawings, the system there illustrated comprises a receiver of the superheterodyne type including an antenna and ground system llll I, connected to a radio-frequency amplifier 12, which is connected in cascade with an oscillator-modulator I 3, an intermediate-frequency amplifier H, a

for deflecting the beam in a direction normal to the direction of deflection effected by the plates 26. The output of the video-frequency amplifier is connected to the control grid 2| by way of the coupling condenser 28 and isolating resistance 29 for controlling the intensity of the cathode ray in accordance with the video-frequencies, as in usual practice.

For developing saw-tooth voltage waves for the plates 26 and saw-tooth current waves for the coils 21, to effect scanning action by the cathode ray, a line-frequency generator 30 and a picture-frequency generator 3| are provided. The output of the video-frequency amplifier I6 is connected to these generators for controllin or operating them in proper synchronism with the scanning at the transmitter. The generators may be of any well-known or suitable design, such as, for instance, that described in copending application, Serial No. 5,781, filed February 9, 1935. The generators, however, are not limited to any particular type, and furthermore, by virtue of the automatic fade-out control system of this invention, presently to be described in detail, the generators, instead of being continuously operative, as has heretofore been the practice, may be entirely controlled or driven by the output voltage of the video-frequency amplifier so as to operate only when proper synchronizing-frequency impulses are being supplied thereto.

For supplying operating potentials to the various electrodes of the tube N, there is provided a voltage divider 32, adapted for connection to a suitable direct-current power source, not shown, and the several electrodes are connected to appropriate taps on the divider. Certain of these taps, as, for instance, 32a, 32b and 320, for the control grid 2 I, the screen 22 and the first anode 23, respectively, are preferably manually adjustable for regulating the initial bias voltages applied to these electrodes and for controlling the operation of the system, as will be presently more fully described. Current for the cathode heater i9 may be supplied in a conventional manner by a suitable circuit, not shown.

There is also provided a sound-frequency channel connected to the output of the oscillatormodulator l3 and comprising, in cascade, an

intermediate-frequency amplifier 33, a detector 35, the audio-frequency amplifier 35 .and sound reproducer 36.

Since the system of Fig. 1, as thus .far described, is, in general, conventional and well understood in the art, a detailed explanation of its general operation is deemed unnecessary. Briefly, however, the visionand sound-modulated carrier waves intercepted by the antenna lB- ii are selected and amplified in the radiofrequency amplifier I2 and supplied to the oscillator-modulator l3, where the signals are converted to intermediate frequencies in the usual manner. The output of the oscillator-modulator is delivered to the intermediate-frequency amplifiers l4 and 33. The amplifier I4 is tuned to select a vision-modulated intermediate-frequency carrier which, in systems where alternate carriers are modulated, respectively, by vision frequencies and sound frequencies, will be spaced of the order of one or more megacycles from the sound-modulated intermediate-frequency carrier, to which the amplifier 33 is tuned. The selected frequencies are amplified in theamplifiers i4 and 33 and supplied therefrom to the detectors l5 and 34, respectively.

The detector 34 produces the audio frequencies of'modulation of the sound carrier and supplies them to the audio-frequency amplifier 35 whereby they are amplified and supplied inthe usual manner to the loudspeaker 36 for reproduction.

It should be here noted that the detector ii of the television channel is designed to develop in its output and deliver to the amplifier l6 videofrequencies corresponding to the envelope of av vision-modulated carrier, particularly a selfsynchronizing, negatively modulated carrier, for the reception of which the receiver of this invention is especially applicable. The video-frequency output or envelope of such a negatively modulated carrier is graphically shown in Fig. 2a. Here, the impulse peaksfor synchronizing the lineand picture-frequency generators are shown at l and 1) respectively, and between the line impulse peaks the variations in amplitude represent the video-frequency details of each line. The maxima in the envelope correspond to black and the minima correspond to white, in the scene.

The video-frequencies of modulation derived from the television, carrier by the detector I5 are supplied to the video-frequency amplifier 16 wherein they are amplified and supplied in the usual manner to the control grid 2! of the oathode-ray tube and to the scanning generators 30 and 3!.

In certain forms of the present invention, which will be hereinafter described, a peak rectifier is employed for selectively producing the automatic fade-out control voltage in accordance with synchronizing impulses present in the modulation voltage output of the video-frequency amplifier. This rectifier, aswill be seen later, functions in the Well-known manner to develop a unidirectional voltage proportional to the amplitude of the synchronizing impulse components in the output of the video-frequency amplifier, as indicated by the line DC in Fig. 2b.

With the proper potentials supplied to the electrodes of tube I1, an electron beam is emitted from the cathode 20 and its intensity is modulated or controlled by the grid 2|, in accordance with the video-frequency voltages impressed thereon. The screen 22 serves to control the average intensity of the beam in a manner hereinafter to be explained, while the first anode 24 cooperates with the second anode 25 to accelerate and focus the electron beam.

Saw-tooth voltage waves are generated in the line-frequency generator and applied to the plates 26 to produce an electrostatic field to deflect the beam in one direction, while saw-tooth current Waves are generated in the picture-frequency generator 3i and are applied to the coils 21 to produce a magnetic field of saw-tooth wave form to deflect the beam in a direction normal to the deflection by the plates 26. The wellknown rectilinear scanning pattern is thus traced on the screen by the beam. In accordance withto. The operation of the generators 30 and 3| is controlled and synchronized with the corresponding scanning actions at the transmitter by the impulse components of the modulation frequencies supplied by the amplifier l6. Suitable selective circuits, not shown, may be provided in the input circuits of the generators 30 and 3|, in the usual manner, for discriminating against undesired impulse frequencies.

Referring now more particularly to the portion of the system of Fig. 1 embodying the present invention, an automatic fade-out control positive bias voltage is derived by rectification of a part of the line-frequency saw-tooth voltage output of the scanning generator 30.' For this purpose a rectifier 31 is provided, having an anode 38 and a cathode 39, the anode being connected to the high voltage output terminal of the generator 30 through a resistance 40 and a coupling condenser 41 and to ,the adjustable tap'32b on the voltage divider 32 through an isolating resistor 43. The cathode 38 is connected to ground through a condenser 42. A resistor 44 is con nected across the rectifier 31 to develop the automatic fade-out control bias voltage output of this rectifier. An initial positive biasing potential is applied to the screen 22 from thetap 321) on the voltage divider, through the path which includes the resistors 43 and 44.

The biasing potential which is applied to the screen 22 from the tap 32b is of such magnitude and polarity that the electron beam is normally insufiicient to illuminate the fluorescent screen. Whenever the generator 30 is in operation, however, an additional bias voltage is developed by the rectifier 31 across the resistor 44, and this voltage is applied positively to the' screen 22 so as to raise-its potential. and permit the beam to become sufficiently intense to illuminate the fluorescent screen.

The output voltage of the rectifier 31 may or may not be proportional to the amplitude of the received vision-modulated carrier wave, according to the design of the generator 30. As above mentioned, in this embodiment of the invention the generator 30 is preferably so designed that the amplitude of the periodic voltage developed therein and supplied to the rectifier 31 is substantially independent of the amplitude of the control voltage supplied to it from the video-frequency amplifier 16, unless such control voltage falls below a predetermined minimum, as disclosed in aforementioned copending application, Serial No. 5,781. Hence, the input voltage to the rectifier 31 will be supplied only when the generator 30 is operating, and automatic fade-out control voltage will be developed for illuminating the screen 25 of the tube 11 only in the presence of a received signal and without appreciable gradation in the control of the screen illumination. It will also be appreciated that the farther removed the automatic fade-out control detector is from the system input, the more independent will be the amplitude of the automatic fade-out control bias from the amplitude of the received carrier and the more effective will be the protection of the cathode-ray tube by the automatic fade-out control.

For the purpose of controlling the contrast of the picture detail, a unidirectional bias voltage is derived by rectification of the intermediate-frequency carrier by the detector I5, and is supplied to the control grids of one or more of the amplifying'tubes of the intermediate-frequency amplifier l4. This automatic contrast control bias voltage is a negative voltage proportional to the amplitude of the received carrier and its applicaknown automatic amplification control systems of sound broadcast receivers, such, for example, as that shown in U. S. Patent No. 1,879,863 to Harold A. Wheeler. It is chiefly in its cooperative relation with the above-described automatic fade-out control that the present invention is concerned with the automatic contrast control. In various of the systems embodying the present invention, in order that the automatic fade-out control voltages may be developed at proper amplitudes to function correctly, it is necessary that the automatic contrast control function so as properly to control the degree of amplification of the received carrier.

Where the receiver just described is employed in systems in which alternate carrier waves have vision and sound modulation, respectively, and the receiver is properly tuned, the output of the amplifier 33 will be detected, amplified and reproduced as sound in the manner aforedescribed. When, however, the receiver is being tuned through a range of such alternate carriers, visionand sound-modulated intermediate-frequency 'carriers will be present alternately in each of the amplifiers l4 and 33. As has been seen, the automatic fade-out control will prevent the screen 25 from being illuminated when a sound-modulated carrier is present in the amplifier 14, since such a carrier will not have the proper frequency components of modulation for efiecting scanning and operation of the automatic fade-out control.

On the other hand, by virtue of a further arrangement provided by the present invention, the reproduction of noisy television signals by the sound reproducer is prevented when the visionmodulation frequencies are present in the sound channel of the receiver. This arrangement comprises amplifying, selecting and detecting means, arranged to control the audio-frequency amplifier 35. A part of the audio-frequency output of the detector 34 is supplied through a coupling condenser 46 to the grid 41 of a tube 45. In the plate circuit of the tube 45 is efiectively included a selective circuit 48, which is tuned to the linescanning frequency of the vision-modulated carrier and comprises a condenser 49 and an inductance 50 coupled to a coil connected in the plate circuit. The tuned circuit 48 is connected to a diode rectifier which may comprise an auxiliary anode 52 and the cathode 53 of the tube 45, which, as illustrated, may be of the diode-triode type. The load circuit of the rectifier 52-53 comprises a resistor 54 and by-pass condenser 55. Suitable operating potentials are applied to the plate 56 and grid 41 of the tube 45, as by batteries 51 and 58, respectively, and a blocking resistor 59 may be interposed in the connection to the grid 41.

When vision-modulated intermediate frequencies are present in thev amplifier 33 and are rectified by the detector 34, a part of the output of the detector is impressed upon the grid 41 through the condenser 46 and amplified in the triode section of the tube 45. Voltage of the linescanning frequency is then developed across the circuit 48 and rectified by the diode 52-58, producing a unidirectional biasing voltage across the resistor 54 in the well-known manner. This biasing voltage is applied negatively, by way of the isolating resistor 35a, to the control gridof one or more of the tubes in the audio-frequency amplifier 35 and acts to suppress the audioirequency amplifier 35 and to silence the loudspeaker 38.

It will be apparent that, in the system described with reference to Fig. 1, the automatic fade-out control, the automatic contrast control and the automatic sound control means cooperate to permit tuning and control oi the sound and vision channels of the receiver by a single control means, that is, the usual tuningv control, not shown. Furthermore, the sound control means of the present invention obviously may be employed in any system where soundmodulated and vision-modulated signals are present, even though they do not comprise alternate carriers and even though the soundand visionreceiving channels are tunable separately and independently.

In Figs. 3, 4 and there are illustrated television receivers embodying modified forms of the invention. In each of these figures there is shown an antenna circuit l8--ll for receiving and supplying the modulated carrier waves to a carrierfrequency amplifier indicated schematically at 82. This amplifier may be a tuned radio-frequency amplifier, but preferably comprises a .ladio-frequency amplifier, a superheterodyne detector, and an intermediate-frequency amplifier, similar to the corresponding sections described with reference to Fig. 1. Further, as in Fig. 1, in each of Figs. 3, 4 and 5 there is provided a detector l5, video-frequency amplifier l8, cathode-ray tube l1 and line-frequency and picture-frequency generators 38 and 3|, which, except as hereinafter noted, are connected in the same manner as the corresponding parts of Fig. 1.

It will be noted that in each of these three figures the cathode-ray tube I! has, for convenience, been indicated schematically, but it will be understood that the tube and the circuits employed in connection therewith are substantially the same as the corresponding parts illustrated in, and described in connection with, Fig. 1. Likewise, the synchronizing-frequency generators 38, 3| shown in Figs. 3-5, may be substantially like those of Fig. 1.

While in the systems of Figs. 3, 4 and 5 sound receiving and reproducing systems have not been shown, it will be understood that, if desired, such systems may be provided as parts of the receivers, as described with reference to the embodiment of the invention shown in Fig. 1, and may include automatic sound control means cooperating with the automatic fade-out control and automatic contrast control arrangements of the three embodiments in question.

Referring now particularly to Fig. 3, there is illustrated an embodiment of the invention whereby greater automatic fade-out control and automatic contrast control bias voltages and selective operation of these controls are obtained by amplifying and selecting a particular characteristic of the video-frequency amplifier output. A part of the output of the amplifier I8 is supplied by way of a coupling condenser 63 and an isolating resistor 84 to the control grid of a tube 65, which is preferably a conventional pentode type amplifier. The cathode circuit of tube 65 may include a biasing resistor 86 and,

by-pass condenser 81, while a blocking resistor 88 may be included in the connection to the plate source, indicated as +3 in the usual manner. The output of the tube 65 is impressed upon a primary winding 88 of a transformer, the secondary winding 18 of which is tuned by a condenser to the fundamental of the line-frequency scanning impulses, thereby furnishing particular selectivity to this frequency. The voltage developed across the circuit 18-11, which is a maximum for such frequency, is rectified by a diode 12, the load circuit of which includes series-connected resistors 18 and 14 individually shunted by by-pass condensers 15 and 18, re-

as described with reference to Fig. 1.

rectional voltage, ordinarily furnished from the main direct-current power supply, but here represented as furnished by battery 18a is applied to the control electrode to provide an initial bias. At the same time, a second unidirectional bias voltage is developed across the resistor 13 which is applied negatively, through a large time-constant circuit including a series resistor 18 and a by-pass condenser 88, to the control grid of one or more, of the tubes of the carrier-frequency amplifier 82, to provide automatic contrast control for the system.

It is believed that the operation of the automatic fade-out control and automatic contrast control of the receiver of Fig. 3 will be obvious, in view of the detailed description hereinbefore set forth with regard to the operation of the corresponding controls of the receiver of Fig. 1. The distinguishing characteristics of the receiver of Fig. 3 are that the rectified automatic fade out control and automatic contrast control voltages are both obtained by rectifying, in a single tube, an amplified and selected part of the video-frequency amplifier output. With this arrangement, the rectified automatic fade-out control voltages are proportional to the received carrier.

In Fig. 4 a television receiving system is shown which embodies a form of the invention in which a single detector performs the functions of developing the video-frequencies of modulation, as well as unidirectional automatic fade-out control and automatic contrast control voltages. In this arrangement, the output of the amplifier 82 is rectified by a diode detector 8| comprising an anode 82 and cathode 83. The load circuit of the rectifier 8| comprises serially-connected resistors 84 and 85 across which are individually connected the condensers 86 and 81, respectively. The junction between condensers 86 and 81 and resistors 84 and 85 is grounded. A lowpass filter is provided by a series inductance 88, shunt condensers 81, 89, and shunt resistors 85 and 98, across which are developed both the unidirectional automatic fade-out control and the modulation voltages, including the video-frequencies and synchronizing frequencies. The modulation-frequency output of this filter is connected through coupling condensers ill, 92 and A unidi- 93 to the amplifier I6, generator 3|, and generator 30, respectively, The unidirectional voltage component or the output of this filter, developed across the resistor 90, is proportional to the amplitude 01 the carrier output of the amplifier 82. This voltage is applied positively, by way of a large time-constant circuit including a series resistor 94 and a by-pass condenser 95, and through a suitable blocking resistor 85a, to a control electrode, preferably the control grid of the cathode-ray tube H to provide automatic fade-out control In substantially the same manner as described with reference to Figs. 1 and 3. A unidirectional voltage, ordinarily furnished from the main direct-current power supply, but

here represented as furnished by battery 90a is applied to the control grid of the tube H to provide an initial bias voltage. The large time-constant circuit in this instance serves to cut oil the modulation frequencies supplied from the detector 8|, so that they will not affect the operation of the automatic fade-out control.

A second unidirectional voltage, which is also proportional to the amplitude of the carrieroutput of the amplifier 62, is developed across the resistor 84 and is applied negatively, by way of a large time-constant circuit including a series resistor 96 and a by-pass condenser 97, to the control grids of one or more of the tubes of the amplifier 62, to provide the automatic contrast control in substantially the same manner as in the previously described embodiments of the invention. It will be seen that in the embodiment of Fig. 4, a single detector serves to supply the video-frequencies as well as the unidirectional automatic fade-out control and automatic contrast control voltages. Here, however, there is no selectivity with regard to the frequencies from which the automatic fade-out control voltages are produced, and it is assumed that this arrangement will be employed only where all of the carrier frequencies of the spectrum through which the receiver is tunable are vision-modulated as distinguished from systems wherein this spectrum is occupied by carriers some of which are modulated by sound and some by vision frequencies.

In Fig. ,5, a television receiver is illustrated which embodies still another form of the invention. In this embodiment, the automatic fadeout control and automatic contrast control unidirectional voltages are derived from an output of the video-frequency amplifier I6. For this purpose, a portion of the output voltage from a point in the video-frequency amplifier I6 at which the impulse peaks are positive relative to ground is supplied, through a coupling condenser 98, to a diode rectifier 99 comprising an anode I and a cathode IOI. The load circuit of the rectifier 99 includes a resistor I02 shunted by a condenser I03. The remainder of the load circuit is constituted by a resistor I04. The unldirectional voltage developed across the resistor I02 is applied positively, through a large timeconstant circuit including a series resistor I and a by-pass condenser I06, to a control electrode of the cathode-ray tube I! to provide automatic fade-out control therefor in the same manner as in the aforedescribed embodiments of the invention.

The unidirectional voltage developed across the resistor I04 is applied negatively, by way of a large time-constant circuit including a series resistor I01 and a by-pass condenser I08, to the control electrodes of one or more of the tubes of the amplifier 62. as described with reference to the other automatic contrast control circuits.

The diode tube 99 and its circuit connections provide a peak detector the operation or which is well known, so that a detailed description thereof is deemed unnecessary here. Reference, however, may be had to United States Patent No. 1,951,685 granted March 20, 1934, upon the application of Harold A. Wheeler, for a full description of the operation of such a detector. Such a peak detector as here utilized provides a unidirectional voltage which is proportional to the amplitude oi! the synchronizing impulses present in the modulation voltage impressed thereon from the video-frequency amplifier. The derivation of such voltages will be readily understood when it is considered, as hereinbefore pointed out, that the result of applying the modulation voltage illustrated in Fig. 2a to a peak type of detector, is to develop a unidirectional voltage proportional to the peak values of the applied voltage, as is indicated, for instance, by the line DC in Fig. 2b. The diode detector is therefore poled so that its input voltage, during the occurrence of impulse peaks, will make the anode oi. the detector positive relative to the cathode and thus develop across the load circuit,

that is, the resistors I03 and I04, unidirectional voltages which are proportional to the value oi. these peak impulses.

In the arrangement described with reference to Fig. 5, it is assumed that the amplitude of the impulse peaks relative to the unmodulated carrier amplitude, that is, the impulse percentage modulation, is uniform for all of the television signals which may be tuned in. Thus, the bias developed by the detector 99 is, for all stations received, proportional to the carrier amplitude of the output of the amplifier i5. Since this is the same condition as with the rectifier of Fig. 3, which is utilized to develop the automatic fadeout control and automatic contrast control bias, the same type of control is accomplished in the receiver of Fig. 5 as in the receiver of Fig. 3. By adjusting the peak detector so that only synchronizing modulation impulses are rectified, the functioning of the automatic fade-out control is made selective so that the positive automatic fade-out control bias voltage is not developed and no background illumination is provided for the screen unless a properly modulated television carrier is being received. Hence, the scanning generators in this embodiment also may be controlled by the video-frequency amplifier output to operate only when a properly modulated carrier is being received.

While we have described what we at present consider the preferred embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from our invention, and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What is claimed is:

1. A television receiving system for carrier waves of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting, amplifying and detecting a received wave of said type to derive therefrom the modulation voltages, a. cathode-ray tube, means for exciting an electrode of said tube with the video-frequency components of said modulation voltages to control the intensity of the cathode ray, means comprising line-frequency and picture-frequency scanning generator circuits controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning by said cathode ray, said cathode-ray tube having an additional electrode for controlling the average intensity of said cathode ray, a large time-constant rectifier circuit excited from the line-frequency generator circuit and including a resistor in its output circuit, and a biasing circuit for said additional electrode including a source of biasing voltage inefiective to establish or maintain the cathode ray and including also said resistor, so connected and proportioned that the resultant voltage oi.

said bias circuit is effective to initiate said cathode ray only during operation of said line-frequency generator.

2. A television receiving system for carrier waves of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting, amplifying and detecting a received wave or said type to derive therefrom the modulation voltages, a screen, and a source of a scanning beam there-' for, means controlled by the synchronizing-frequency components of said modulation voltages for eiTecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for effecting variations in the intensity of said beam to reproduce a scene, an auxiliary amplifier connected to amplify a portion of said modulation voltages, a rectifier, and a selective circuit, tuned to said line-frequency modulation component, coupling said amplifier and said rectifier, and means for utilizing the output of said rectifier for modifying the average intensity of said beam.

3. A television receiving system for carrier waves of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting, amplifying and detecting a received wave to derive therefrom the modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for effecting variations in the intensity of said beam to reproduce a scene,

a peak voltage rectifier for rectifying the modulation voltages to derive therefrom a unidirectional voltage, and means for utilizing said unidirectional vpltage for controlling the average intensity of said beam.

4. A television receiving system for carrier waves of the type having modulation including video-frequency and line-frequency-synchronizing and picture-frequency-synchronizing components, comprising means for selecting, amplifying and detecting a received wave to derive therefrom the modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by said synchronizing-frequency components of the modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for effecting variation in the intensity of said beam to reproduce a scene, a peak voltage rectifier, means for supplying said line-frequency-synchronizing components to said rectifier to develop a unidirectional voltage of an amplitude substantially equal to the amplitude of said linefrequency-synchronizing components, and means for utilizing said unidirectional voltage for controlling the average intensity of said beam.

5. A television receiving system for carrier waves within a wide range of intensities and of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting, amplifying and detecting a received wave of said type to derive therefrom the modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components o said modulation voltages for effecting variations in the intensity of said beam to reproduce a scene,

an auxiliary amplifier connected to amplify a portion of the output of said amplifying means, a rectifier, and a selective circuit, tuned to a frequency of one of said modulation voltages, coupling said amplifier and said rectifier, means for utilizing a part of the output of said rectifier for controlling the average intensity of said beam, and means for utilizing another part of the output of said rectifier for maintaining the amplitude of said modulation voltages within a narrow range relative to that of thereceived signals.

6. A television receiving system for carrier waves within a wide range of intensities and of the type having modulation'including video-frequency and synchronizing-frequency components, comprising means for selecting and amplifying a received wave of said type, means for detecting the output of said amplifying means to derive therefrom the modulation voltages, a screen, a source of electrons for providing a scanning beam for said carrier wave, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for efl'ecting variations in the intensity of said beam to reproduce a scene, an auxiliary amplifier connected to amplify a portion of the output of said amplifying means, a rectifier, and a selective circuit, tuned to the line-frequency modulation component, coupling said amplifier and rectifier, means for utilizing a part of the output of said rectifier for modifying the average intensity of said beam, and means for utilizing another part of the output of said rectifier for maintaining the amplitude of said modulation voltages within a narrow range relative to that of the received signals.

7. A television receiving system for carrier waves of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting and amplifying a received wave of said typ a single rectifier for deriving from the amplifier carrier wave the modulation voltages and a plurality of unidirectional voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for eifecting variations in the intensity of said beam to reproduce a scene, means controlled by one of said unidirectional voltages for modifying the average intensity of the beam, and means controlled by another of said unidirectional voltages for maintaining the amplitude of said modulation voltthe received signals.

8. A television receiving system for carrier waves of the type having modulation including video-frequency and synchronizing-frequency components, comprising means for selecting, amplifying and detecting a received wave of said type to derive therefrom the modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for eflecting scanning of said screen by said beam, means responsive to the videofrequency components of said modulation voltages for effecting variations of the intensity of said beam to reproduce a scene, a peak detector connected to the output of said amplifying means for producing unidirectional voltages, means for utilizing one of said unidirectional voltages for modifying the average intensity of the beam, and means for utilizing another of said unidirectional voltages for maintaining the amplitude of said modulation voltages within a narrow range relative to that of the received signals.

9. A television receiving system for carrier waves of a first type having modulation comprising sound frequencies and carrier waves of a second type having modulation including video-frequency and synchronizing-frequency components, comprising a common means for selecting and amplifying received waves of both of said types, an audio channel including means for detecting the amplified waves of said first type to derive therefrom audio-frequency modulation voltages, means for converting said audiofrequency voltages into sound, a video-frequency channel including means for detecting the amplified waves of said second type to derive therefrom the video-frequency modulation voltages and synchronizing-frequency modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for effecting variations in the intensity of said beam to reproduce a scene, means operative in accordance with the operation of said scanning means for modifying the average intensity of said beam, and means responsive to the presence of video-frequencies in said audio channel for preventing the reproduction of sound.

10. A television receiving system for carrier waves of a first type having modulation comprising sound frequencies and carrier waves of a second type having modulation including videofrequency and synchronizing-frequency components, comprising a common means for selecting and amplifying received waves of both of said types, an audio channel including means for detecting the amplified waves of said first type to derive therefrom audio-frequency modulation voltages, means for converting said audio-frequency voltages into sound, a videochannel including means for detecting the amplified waves of said second type to derive therefrom video-frequency and synchronizing-frequency modulation voltages, a screen, a source of a scanning beam for said screen, means controlled by the synchronizing-frequency components of said modulation voltages for effecting scanning of said screen by said beam, means responsive to the video-frequency components of said voltages for efi'ecting variations in the intensity of said beam to reproduce a scene, means operative in accordance with the operation of said scanning means for modifying the average intensity of said beam, means responsive to the amplitude of the received carrier of the second said type for maintaining the amplitude of said modulation voltages thereof within a narrow range relative to that of said received carrier, and means responsive to the presence of videofrequencies in said audio channel for preventing the reproduction of sound.

11. A television receiving system for carrier waves of a first type having modulation including video-frequency and synchronizing-frequency components, and carrier waves of a second type having modulation comprising sound frequencies, comprising a common means for selecting and amplifying carrier waves of both of said types, oscillator-modulator means for heterodyning said carrier waves, means for amplifying the intermediate-frequency voltages derived by said heterodyning from the carrier waves of said first type, detecting and amplifying means for said intermediate-frequency voltages to derive the modulation voltages, a screen, a source of electrons for producing a scanning beam for said screen, means controlled by the synchronizing-frequency component of said modulation voltages for efiecting scanning of said screen by said beam, means responsive to the video-frequency components of said modulation voltages for effecting variations in the intensity of said beam to reproduce a scene, means operative in accordance with said scanning means for modifying the average intensity of said beam, means for amplifying the intermediate-frequency voltages derived by said heterodyning means from the carrier waves of said second type, detecting and amplifying means for the last said intermediate-frequency voltages to derive therefrom audio-frequency voltages, means for amplifying and reproducing said audio-frequency voltages, means connected to the output of the audiofrequency detecting means for selecting videofrequencies therefrom and for producing a unidirectional voltage, and means for utilizing said unidirectional voltage to suppress amplification in said audio-frequency amplifying means.

HAROLD M. LEWIS. MADISON CAWEIN.

DlSCLAlMER 2,137,123.Har0ld M. Lewis, Douglaston, Long Island, and Madison Gawain, Manhasset, N. Y. TELEVISION SYSTEM. Patent dated November 15, 1938. Disclaimer filed June 17, 1940, by the inventors; the assignee, Hazelt'ine Corporation, assenting.

Hereby enter this disclaimer to the subject matter of claim 3 and the subject matter of claim 4 insofar as the phrase amplitude of said line-frequency-synchronizing components is construed to refer to the amplitude of said line-frequency-synchronizing components as modified by other components of the television signal, such as the unidirectional background-illumination components thereof.

[Qfiic'ial Gazette July 9, 1940.]

DISCLAIMER 2,137,123.Harold M. Lewis, Douglaston, Long Island, and Madison Gawain, Manhasset, N. Y. TELEVISION SYSTEM. Patent dated November 15, 1938. Disclaimer filed June 17, 1940, by the inventors; the assignee, Hazeltine Corporation, assenting.

Hereb enter this disclaimer to the subject matter of claim 3 and the subject matter of 4 insofar as the phrase amplitude of said line-frequency-synchronizing components is construed to refer to the amplitude of said line-frequency-synchronjzing components as modified by other components of the television signal, such as the 'directional background-illunfination components thereof.

[Oficial Gazette July 9, 1940.] 

